The present invention relates to displaying cardiological data, and more specifically to methods and apparatus for displaying alternans data of an electrocardiogram (“ECG”) signal.
Alternans are subtle beat-to-beat changes in the repeating pattern of an ECG signal. Several studies have demonstrated a high correlation between an individual's susceptibility to ventricular arrhythmias and sudden cardiac death and the presence of a T-wave alternans (“TWA”) pattern of variation in the individual's ECG signal.
While an ECG signal typically has an amplitude measured in millivolts, an alternans pattern of variation with an amplitude on the order of a microvolt may be clinically significant. Accordingly, an alternans pattern of variation is typically difficult and time consuming to detect by visual inspection of the ECG signal. Instead, electronic detection and quantification of the alternans pattern of variation is necessary. Such electronic detection and quantification of the alternans pattern of variation is complicated by the presence of noise in the ECG signal. Noise may result in beat-to-beat variations that have a larger magnitude than the alternans pattern of variation.
Current techniques used to quantify patterns of variation in alternans data compensate for at least some of the noise in the ECG signal. However, artifacts resulting from a patient's movement (e.g., pedaling, footfalls, and the like) and/or respiration during exercise or Holter testing may nevertheless interfere with a clinician's assessment of the patterns of variation in the alternans data. These artifacts often overlay the patterns of variation in the alternans data.